1. Field of the Invention
The present invention relates to a method for forming an armrest for an automotive seat, and more particularly to a method of such foaming type wherein a base foaming urethane material in liquid is injected into a preformed three-dimensional trim cover assembly within a foaming die and then foamed therein to attain an armrest body for use on an automotive seat.
2. Description of Prior Art
There has been known such type of armrest, as shown in FIG. 1, which is rotatably secured in a predetermined storage space (O) between two seat backs (SB) (SB) of an automotive seat. This armrest (AR') has a support shaft (1') which is rotatably secured, at both ends (1'a)(1'a) thereof, to each of the seat backs (SB), allowing the armrest body to be rotatable vertically about the shaft (1') as indicated by the arrows.
As can be seen in FIGS. 1 and 2, this conventional armrest (AR') comprises a trim cover assembly (3'), a foam cushion member (4), a generally U-shaped frame (2) and the foregoing support shaft (1'). The shaft (1') has been welded in the two holes (21a) formed respectively in the flattened end portions (21) of the frame (2), such that both two ends (1'a) of shaft (1') extend outwardly from the respective lateral frame sections of frame (2). The trim cover assembly is preformed generally in a three-dimensional manner to assume a closed box-like configuration, having two through-holes (32) formed in the respective lateral sides (3'a) thereof and an elongated slit (3h) formed in the rearward side (3'b) thereof. Designation (33) stands for a hole into which an injection nozzle is inserted for a foaming purpose. The process for forming the armrest (AR') is such that a worker uses his or her hands to insert the frame (2) into within the preformed three-dimensional trim cover assembly (3') by inserting both curved part of the frame (2) and support shaft (1') through the elongated slit (3h) into the trim cover assembly (3'), and then expose the two outwardly projected ends (1'a) of shaft (1') out of the respective two through-holes (32) of trim cover assembly (3'), after which, the thus-prepared armrest (3') is set in a foaming die (as seen in FIG. 8), with an injection nozzle (N) being inserted through the hole (33) into within the trim cover assembly (3'), and a base foaming material (4') in liquid is injected from the nozzle (N) and filled in the trim cover assembly (3'). Then the liquid foaming material is cured therein to form a foam cushion member (4) so as to obtain such armrest body (AR') shown in FIG. 1.
However, this prior-art method has been found defective in that, because of the entire length (W1) of shaft (1') being greater than the width (W2) of elongated hole (3h), it is difficult to smoothly insert both ends (1'a) of shaft (1') through the hole (3h) into within the trim cover assembly (3) and even more difficult to quickly pass both shaft ends (1'a) through the respective through-holes (32) outwardly of the trim cover assembly (3'). In worst case, it causes a break or tear in the edges of both elongated hole (3h) and through-holes (32), or at any portion of trim cover assembly (3) where a worker's hand force is greatly exerted, resulting in the leakage of a liquid foaming material (4') through such break and tear during a foaming process. Also, the liquid foaming material (4') is leaked through the elongated slit (3h) to the outside of armrest (AR').
In addition, most of the trim cover assembly employed for this forming of armrest is of the lamination structure wherein a wadding layer of slab urethane foam material is laminated on the inner surfaces of a top cover layer for a soft-touch effect, and thus it has been proposed to attach a synthetic resin film (f), as shown in FIG. 1, to the surface of that wadding layer, which is disclosed by the Japanese Granted U.M. Pubs. Nos. 4-790 and 5-44100 for instance, whereby a base foaming material in liquid is prevented by the film from being impregnated into the foam wadding layer in the foaming process, and therefore, the liquid foaming material will not be cured in the soft wadding layer, thus maintaining soft touch of armrest body. But, even in that case, as the film (f) itself is impermeable, the whole air permeable effect of armrest body occupied by the permeable materials, i.e. top cover layer, foam wadding layer and foam cushion member, is deteriorated by the film (f), as a result of which, a cushioning degree of armrest body is extremely decreased, and when stored in the storage space (see the designation (O) in FIG. 1) between the seat backs (SB), the surface area (3'c) of armrest (3'), on which the back of passenger contacts, does not give any optimal ventilation to absorb sweat or wet from the passenger's back, which makes the passenger feel discomfort at his or her back.